I admittedly never finished Tunic, but that does not seem to fit the refined metroidbrania criteria? While there are shortcuts that can be had with fore-knowledge, the game has quite a bit of traditional metroidvania in that you need utility item X to advance past y. While there are rules and systems to be discovered from the manual, the game is still a version of get the dynamite, to unlock the boomerang, to get the wand, to unlock the final door.

Outer Wilds is a much stronger fit for the category where the entire world is accessible from the start.